With techniques of the prior art, the withdrawal of liquid through an outlet of a tank on a spacecraft (e.g., the withdrawal of liquid propellant from a fuel tank for delivery to the thrusters of the spacecraft, or for transfer to another fuel tank on a different space vehicle) in a low-gravity environment would typically involve unstable flow of the liquid propellant at the tank outlet, which tended to entrap bubbles of gas or vapor in the liquid being withdrawn from the tank.
A need has been perceived in the prior art for an apparatus operable in a low-gravity environment for enabling liquid to be withdrawn through an outlet of a tank at a controlled rate, whereby the flow of liquid through the outlet can proceed in a regular and generally unbroken current so as to inhibit entrapment of gas or vapor in the liquid that is being withdrawn from the tank.